Validated builders for ClickHouse-specific migration column types that have no direct Ecto.Migration.add/3 equivalent.

Ecto.Migration.add/3 rejects any Ecto.Type/Ecto.ParameterizedType module as a column type, so a type like Ecto.Adapters.ClickHouse.Types.FixedString can never be given to it directly -- only atoms, quoted atoms, composite tuples, and references(...) are accepted. These builders produce the quoted-atom form add/3 does accept, with the parameter validated up front instead of only surfacing as a ClickHouse DDL error at migration time:

add(:code, Ecto.Adapters.ClickHouse.Migration.fixed_string(16))
add(:status, Ecto.Adapters.ClickHouse.Migration.low_cardinality(:string))

FixedString(N) additionally has a full Ecto.ParameterizedType -- Ecto.Adapters.ClickHouse.Types.FixedString -- for the schema side, where add/3's restriction doesn't apply:

field :code, Ecto.Adapters.ClickHouse.Types.FixedString, size: 16

LowCardinality(T) doesn't get one: it's transparent to callers (decoded to the same Elixir value T would decode to on its own), so a plain field :status, :string already works. Map(K, V) gets neither a builder nor a ParameterizedType -- use the quoted atom directly:

add(:m, :"Map(String, UInt32)")

Building a table's options: string

table/2's options: takes a single raw string for everything after the column list -- engine, ORDER BY, PARTITION BY, SETTINGS k = v, .... table_options/1 builds that string from a keyword list instead of requiring migration authors to hand-interpolate and quote it (SETTINGS in particular gets tedious once it accumulates several key/value pairs):

create table(:events, primary_key: false,
  options: Ecto.Adapters.ClickHouse.Migration.table_options(
    engine: "MergeTree",
    partition_by: "toYYYYMM(inserted_at)",
    order_by: "id"
  )
) do
  add :id, :id, primary_key: true
  add :inserted_at, :utc_datetime
end

It also resolves {:system, "ENV_VAR"} settings values from the environment at the time the helper runs (migration-run time, i.e. mix ecto.migrate, not compile time) -- handy for credentials that shouldn't be committed as a literal string in a migration file, like the Kafka-engine example in Ecto.Adapters.ClickHouse.DDL's moduledoc:

execute("""
CREATE TABLE events_queue (id UInt64, payload String)
#{Ecto.Adapters.ClickHouse.Migration.table_options(
  engine: "Kafka",
  settings: [
    kafka_broker_list: {:system, "KAFKA_BROKER_LIST"},
    kafka_topic_list: "events",
    kafka_group_name: "events_consumer",
    kafka_format: "JSONEachRow"
  ]
)}
""")

which renders (given KAFKA_BROKER_LIST=kafka:9092 in the environment the migration runs in) as:

ENGINE = Kafka SETTINGS kafka_broker_list = 'kafka:9092', kafka_topic_list = 'events', kafka_group_name = 'events_consumer', kafka_format = 'JSONEachRow'